1. Field of the Invention
The present invention relates to novel polydiorganosiloxane substituted (grafted) thiuram disulfides, to a process for the preparation of such novel disulfides and to use thereof in the radical polymerization of vinyl monomers.
2. Description of the Prior Art
Makromol. Chem. Rapid. Commun., 3, 127-132 (1982) describes the use of tetraalkylthiuram as an additive during the radical polymerization of vinyl monomers, such additive being designated an "iniferter" because during this polymerization it serves the triple function of free radical initiator, of chain transfer agent and of chain terminator.
U.S. Pat. No. 2,813,849 describes the use, inter alia, of tetraalkylthiuram disulfides as thermal initiators for the polymerization of acrylonitrile, methacrylonitrile, styrene and alkyl methacrylates.
EP-A-237,792 describes a process for the preparation of telechelic polymers by radical polymerization of ethylenic monomers in the presence of thiuram disulfide derivatives or of dithiocarbamate derivatives which have at least one reactive organic functional group.
The above processes, however, do not enable the preparation of polydiorganosiloxane/vinyl polymer/polydiorganosiloxane three-block copolymers utilizing a process of radical polymerization of vinyl monomers.
Indeed, it is well known to this art that, despite their particularly advantageous physicochemical properties, polydiorganosiloxanes must have particularly high molecular weights in order to exhibit adequate mechanical properties. However, even after crosslinking, unfilled polymers exhibit a rupture strength, a tear strength and an elongation which are rather mediocre. One solution to this problem would be to provide block or sequential copolymers having polydiorganosiloxane segments and crystalline or semicrystalline polymeric segments.
Need continues to exist in this art for an industrial process permitting preparation of such copolymers.